Gluten is a vegetable protein having various functions such as dough forming ability, gelation properties with heating and the like, and is widely utilized as main or supplementary raw materials of various food products such as bread, pasta, noodles, fish paste, sausage and the like. However, gluten is insoluble in water at a neutral pH range, while it shows good solubility in water at an acidic pH range. Therefore, utilization of gluten in food products is much limited in this respect.
In order to improve solubility of gluten, various processes such as deamidation [N. Matsutomi et al., J. Agr. Chem. Soc. Jpn., 50, 983 (1981)], chemical modification of side chains [D. R. Grant, Cereal Chem., 50, 417 (1973)] and the like have been hitherto proposed. However, these conventional processes are not suitable for practical use. For example, in deamidation, gluten having sufficient solubility can not be obtained unless a treatment at a high temperature for a long period of time under a very high acid concentration is performed. In case of chemical modification of side chains, much more time and labor are required until safety of the chemical modification is confirmed and the modified product is allowed as a food. Thus, the conventional processes can hardly be employed in practice.
Under these circumstances, in order to find out a practical process for producing gluten having high solubility even at a neutral pH range, the present inventors have intensively studied. As the result, it has been found that solubility of gluten even at a neutral pH range is remarkably improved by heating gluten in an aqueous acidic solution in the presence of another certain protein and then neutralizing the solution after cooling.